@@ -609,19 +609,47 @@ C<.trim> callback has been defined.
This is called during the option negotiation phase to find out if the
plugin wants the C<.zero> callback to be utilized. Support for
-writing zeroes is still advertised to the client (unless the nbdkit
-filter nozero is also used), so returning false merely serves as a way
-to avoid complicating the C<.zero> callback to have to fail with
-C<ENOTSUP> or C<EOPNOTSUPP> on the connections where it will never be
-more efficient than using C<.pwrite> up front.
+writing zeroes is still advertised to the client (unless the
+L<nbdkit-nozero-filter(1)> is also used), so returning false merely
+serves as a way to avoid complicating the C<.zero> callback to have to
+fail with C<ENOTSUP> or C<EOPNOTSUPP> on the connections where it will
+never be more efficient than using C<.pwrite> up front.
If there is an error, C<.can_zero> should call C<nbdkit_error> with an
error message and return C<-1>.
-This callback is not required. If omitted, then nbdkit always tries
-C<.zero> first if it is present, and gracefully falls back to
-C<.pwrite> if C<.zero> was absent or failed with C<ENOTSUP> or
-C<EOPNOTSUPP>.
+This callback is not required. If omitted, then for a normal zero
+request, nbdkit always tries C<.zero> first if it is present, and
+gracefully falls back to C<.pwrite> if C<.zero> was absent or failed
+with C<ENOTSUP> or C<EOPNOTSUPP>.
+
+=head2 C<.can_fast_zero>
+
+ int can_fast_zero (void *handle);
+
+This is called during the option negotiation phase to find out if the
+plugin wants to advertise support for fast zero requests. If this
+support is not advertised, a client cannot attempt fast zero requests,
+and has no way to tell if writing zeroes offers any speedups compared
+to using C<.pwrite> (other than compressed network traffic). If
+support is advertised, then C<.zero> will have
+C<NBDKIT_FLAG_FAST_ZERO> set when the client has requested a fast
+zero, in which case the plugin must fail with C<ENOTSUP> or
+C<EOPNOTSUPP> up front if the request would not offer any benefits
+over C<.pwrite>. Advertising support for fast zero requests does not
+require that writing zeroes be fast, only that the result (whether
+success or failure) is fast, so this should be advertised when
+feasible.
+
+If there is an error, C<.can_fast_zero> should call C<nbdkit_error>
+with an error message and return C<-1>.
+
+This callback is not required. If omitted, then nbdkit returns true
+if C<.zero> is absent or C<.can_zero> returns false (in those cases,
+nbdkit fails all fast zero requests, as its fallback to C<.pwrite> is
+not inherently faster), otherwise false (since it cannot be determined
+in advance if the plugin's C<.zero> will properly honor the semantics
+of C<NBDKIT_FLAG_FAST_ZERO>).
=head2 C<.can_extents>
@@ -804,15 +832,25 @@ bytes of zeroes at C<offset> in the backing store.
This function will not be called if C<.can_zero> returned false. On
input, the parameter C<flags> may include C<NBDKIT_FLAG_MAY_TRIM>
-unconditionally, and C<NBDKIT_FLAG_FUA> based on the result of
-C<.can_fua>.
+unconditionally, C<NBDKIT_FLAG_FUA> based on the result of
+C<.can_fua>, and C<NBDKIT_FLAG_FAST_ZERO> based on the result of
+C<.can_fast_zero>.
If C<NBDKIT_FLAG_MAY_TRIM> is requested, the operation can punch a
hole instead of writing actual zero bytes, but only if subsequent
-reads from the hole read as zeroes. If this callback is omitted, or
-if it fails with C<ENOTSUP> or C<EOPNOTSUPP> (whether by
-C<nbdkit_set_error> or C<errno>), then C<.pwrite> will be used
-instead.
+reads from the hole read as zeroes.
+
+If C<NBDKIT_FLAG_FAST_ZERO> is requested, the plugin must decide up
+front if the implementation is likely to be faster than a
+corresponding C<.pwrite>; if not, then it must immediately fail with
+C<ENOTSUP> or C<EOPNOTSUPP> (whether by C<nbdkit_set_error> or
+C<errno>) and preferably without modifying the exported image. It is
+acceptable to always fail a fast zero request (as a fast failure is
+better than attempting the write only to find out after the fact that
+it was not fast after all). Note that on Linux, support for
+C<ioctl(BLKZEROOUT)> is insufficient for determining whether a zero
+request to a block device will be fast (because the kernel will
+perform a slow fallback when needed).
The callback must write the whole C<count> bytes if it can. The NBD
protocol doesn't allow partial writes (instead, these would be
@@ -823,6 +861,11 @@ If there is an error, C<.zero> should call C<nbdkit_error> with an
error message, and C<nbdkit_set_error> to record an appropriate error
(unless C<errno> is sufficient), then return C<-1>.
+If this callback is omitted, or if it fails with C<ENOTSUP> or
+C<EOPNOTSUPP> (whether by C<nbdkit_set_error> or C<errno>), then
+C<.pwrite> will be used as an automatic fallback except when the
+client requested a fast zero.
+
=head2 C<.extents>
int extents (void *handle, uint32_t count, uint64_t offset,
@@ -1221,6 +1264,7 @@ and then users will be able to run it like this:
=head1 SEE ALSO
L<nbdkit(1)>,
+L<nbdkit-nozero-filter(3)>,
L<nbdkit-filter(3)>.
Standard plugins provided by nbdkit:
@@ -289,7 +289,10 @@ The script should exit with code C<0> for true or code C<3> for false.
=item C<is_rotational>
+=item C<can_fast_zero>
+
/path/to/script is_rotational <handle>
+ /path/to/script can_fast_zero <handle>
The script should exit with code C<0> for true or code C<3> for false.
@@ -361,12 +364,18 @@ also provide a C<can_trim> method which exits with code C<0> (true).
/path/to/script zero <handle> <count> <offset> <flags>
The C<flags> parameter can be an empty string or a comma-separated
-list of the flags: C<"fua"> and C<"may_trim"> (eg. C<"">, C<"fua">,
-C<"fua,may_trim"> are all possible values).
+list of the flags: C<"fua">, C<"may_trim">, and C<"fast"> (eg. C<"">,
+C<"fua">, C<"fua,may_trim,fast"> are some of the 8 possible values).
Unlike in other languages, if you provide a C<zero> method you B<must>
also provide a C<can_zero> method which exits with code C<0> (true).
+To trigger a fallback to <pwrite> on a normal zero request, or to
+respond quickly to the C<"fast"> flag that a specific zero request is
+no faster than a corresponding write, the script must output
+C<ENOTSUP> or C<EOPNOTSUPP> to stderr (possibly followed by a
+description of the problem) before exiting with code C<1> (failure).
+
=item C<extents>
/path/to/script extents <handle> <count> <offset> <flags>
@@ -404,11 +404,25 @@ plugin_can_zero (struct backend *b, struct connection *conn)
static int
plugin_can_fast_zero (struct backend *b, struct connection *conn)
{
+ struct backend_plugin *p = container_of (b, struct backend_plugin, backend);
+ int r;
+
assert (connection_get_handle (conn, 0));
debug ("can_fast_zero");
- return 0; /* Upcoming patch will actually add support. */
+ if (p->plugin.can_fast_zero)
+ return p->plugin.can_fast_zero (connection_get_handle (conn, 0));
+ /* Advertise support for fast zeroes if no .zero or .can_zero is
+ * false: in those cases, we fail fast instead of using .pwrite.
+ * This also works when v1 plugin has only ._zero_old.
+ */
+ if (p->plugin.zero == NULL)
+ return 1;
+ r = plugin_can_zero (b, conn);
+ if (r == -1)
+ return -1;
+ return !r;
}
static int
@@ -656,15 +670,18 @@ plugin_zero (struct backend *b, struct connection *conn,
}
if (can_zero) {
- /* if (!can_fast_zero) */
- flags &= ~NBDKIT_FLAG_FAST_ZERO;
errno = 0;
if (p->plugin.zero)
r = p->plugin.zero (connection_get_handle (conn, 0), count, offset,
flags);
- else if (p->plugin._zero_old)
+ else if (p->plugin._zero_old) {
+ if (fast_zero) {
+ *err = EOPNOTSUPP;
+ return -1;
+ }
r = p->plugin._zero_old (connection_get_handle (conn, 0), count, offset,
may_trim);
+ }
else
emulate = true;
if (r == -1)
@@ -132,6 +132,8 @@ struct nbdkit_plugin {
int (*cache) (void *handle, uint32_t count, uint64_t offset, uint32_t flags);
int (*thread_model) (void);
+
+ int (*can_fast_zero) (void *handle);
};
extern void nbdkit_set_error (int err);
@@ -349,6 +349,13 @@ data_can_cache (void *handle)
return NBDKIT_CACHE_NATIVE;
}
+/* Fast zero. */
+static int
+data_can_fast_zero (void *handle)
+{
+ return 1;
+}
+
/* Read data. */
static int
data_pread (void *handle, void *buf, uint32_t count, uint64_t offset,
@@ -375,8 +382,10 @@ data_pwrite (void *handle, const void *buf, uint32_t count, uint64_t offset,
static int
data_zero (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
{
- /* Flushing, and thus FUA flag, is a no-op */
- assert ((flags & ~(NBDKIT_FLAG_FUA | NBDKIT_FLAG_MAY_TRIM)) == 0);
+ /* Flushing, and thus FUA flag, is a no-op. Assume that
+ * sparse_array_zero generally beats writes, so FAST_ZERO is a no-op. */
+ assert ((flags & ~(NBDKIT_FLAG_FUA | NBDKIT_FLAG_MAY_TRIM |
+ NBDKIT_FLAG_FAST_ZERO)) == 0);
ACQUIRE_LOCK_FOR_CURRENT_SCOPE (&lock);
sparse_array_zero (sa, count, offset);
return 0;
@@ -423,6 +432,7 @@ static struct nbdkit_plugin plugin = {
.can_multi_conn = data_can_multi_conn,
.can_fua = data_can_fua,
.can_cache = data_can_cache,
+ .can_fast_zero = data_can_fast_zero,
.pread = data_pread,
.pwrite = data_pwrite,
.zero = data_zero,
@@ -129,13 +129,10 @@ full_pwrite (void *handle, const void *buf, uint32_t count, uint64_t offset,
return -1;
}
-/* Write zeroes. */
-static int
-full_zero (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
-{
- errno = ENOSPC;
- return -1;
-}
+/* Omitting full_zero is intentional: that way, nbdkit defaults to
+ * permitting fast zeroes which respond with ENOTSUP, while normal
+ * zeroes fall back to pwrite and respond with ENOSPC.
+ */
/* Trim. */
static int
@@ -172,7 +169,6 @@ static struct nbdkit_plugin plugin = {
.can_cache = full_can_cache,
.pread = full_pread,
.pwrite = full_pwrite,
- .zero = full_zero,
.trim = full_trim,
.extents = full_extents,
/* In this plugin, errno is preserved properly along error return
@@ -147,6 +147,13 @@ memory_can_cache (void *handle)
return NBDKIT_CACHE_NATIVE;
}
+/* Fast zero. */
+static int
+memory_can_fast_zero (void *handle)
+{
+ return 1;
+}
+
/* Read data. */
static int
memory_pread (void *handle, void *buf, uint32_t count, uint64_t offset,
@@ -173,8 +180,10 @@ memory_pwrite (void *handle, const void *buf, uint32_t count, uint64_t offset,
static int
memory_zero (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
{
- /* Flushing, and thus FUA flag, is a no-op */
- assert ((flags & ~(NBDKIT_FLAG_FUA | NBDKIT_FLAG_MAY_TRIM)) == 0);
+ /* Flushing, and thus FUA flag, is a no-op. Assume that
+ * sparse_array_zero generally beats writes, so FAST_ZERO is a no-op. */
+ assert ((flags & ~(NBDKIT_FLAG_FUA | NBDKIT_FLAG_MAY_TRIM |
+ NBDKIT_FLAG_FAST_ZERO)) == 0);
ACQUIRE_LOCK_FOR_CURRENT_SCOPE (&lock);
sparse_array_zero (sa, count, offset);
return 0;
@@ -221,6 +230,7 @@ static struct nbdkit_plugin plugin = {
.can_fua = memory_can_fua,
.can_multi_conn = memory_can_multi_conn,
.can_cache = memory_can_cache,
+ .can_fast_zero = memory_can_fast_zero,
.pread = memory_pread,
.pwrite = memory_pwrite,
.zero = memory_zero,
@@ -633,6 +633,24 @@ nbdplug_can_zero (void *handle)
return i;
}
+static int
+nbdplug_can_fast_zero (void *handle)
+{
+#if LIBNBD_HAVE_NBD_CAN_FAST_ZERO
+ struct handle *h = handle;
+ int i = nbd_can_fast_zero (h->nbd);
+
+ if (i == -1) {
+ nbdkit_error ("failure to check fast zero flag: %s", nbd_get_error ());
+ return -1;
+ }
+ return i;
+#else
+ /* libnbd 0.9.8 lacks fast zero support */
+ return 0;
+#endif
+}
+
static int
nbdplug_can_fua (void *handle)
{
@@ -724,12 +742,19 @@ nbdplug_zero (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
struct transaction s;
uint32_t f = 0;
- assert (!(flags & ~(NBDKIT_FLAG_FUA | NBDKIT_FLAG_MAY_TRIM)));
+ assert (!(flags & ~(NBDKIT_FLAG_FUA | NBDKIT_FLAG_MAY_TRIM |
+ NBDKIT_FLAG_FAST_ZERO)));
if (!(flags & NBDKIT_FLAG_MAY_TRIM))
f |= LIBNBD_CMD_FLAG_NO_HOLE;
if (flags & NBDKIT_FLAG_FUA)
f |= LIBNBD_CMD_FLAG_FUA;
+#if LIBNBD_HAVE_NBD_CAN_FAST_ZERO
+ if (flags & NBDKIT_FLAG_FAST_ZERO)
+ f |= LIBNBD_CMD_FLAG_FAST_ZERO;
+#else
+ assert (!(flags & NBDKIT_FLAG_FAST_ZERO));
+#endif
nbdplug_prepare (&s);
nbdplug_register (h, &s, nbd_aio_zero (h->nbd, count, offset, s.cb, f));
return nbdplug_reply (h, &s);
@@ -831,6 +856,7 @@ static struct nbdkit_plugin plugin = {
.is_rotational = nbdplug_is_rotational,
.can_trim = nbdplug_can_trim,
.can_zero = nbdplug_can_zero,
+ .can_fast_zero = nbdplug_can_fast_zero,
.can_fua = nbdplug_can_fua,
.can_multi_conn = nbdplug_can_multi_conn,
.can_extents = nbdplug_can_extents,
@@ -100,6 +100,13 @@ null_can_cache (void *handle)
return NBDKIT_CACHE_NATIVE;
}
+/* Fast zero. */
+static int
+null_can_fast_zero (void *handle)
+{
+ return 1;
+}
+
/* Read data. */
static int
null_pread (void *handle, void *buf, uint32_t count, uint64_t offset,
@@ -167,6 +174,7 @@ static struct nbdkit_plugin plugin = {
.get_size = null_get_size,
.can_multi_conn = null_can_multi_conn,
.can_cache = null_can_cache,
+ .can_fast_zero = null_can_fast_zero,
.pread = null_pread,
.pwrite = null_pwrite,
.zero = null_zero,
@@ -134,6 +134,8 @@ static value cache_fn;
static value thread_model_fn;
+static value can_fast_zero_fn;
+
/*----------------------------------------------------------------------*/
/* Wrapper functions that translate calls from C (ie. nbdkit) to OCaml. */
@@ -705,6 +707,25 @@ thread_model_wrapper (void)
CAMLreturnT (int, Int_val (rv));
}
+static int
+can_fast_zero_wrapper (void *h)
+{
+ CAMLparam0 ();
+ CAMLlocal1 (rv);
+
+ caml_leave_blocking_section ();
+
+ rv = caml_callback_exn (can_fast_zero_fn, *(value *) h);
+ if (Is_exception_result (rv)) {
+ nbdkit_error ("%s", caml_format_exception (Extract_exception (rv)));
+ caml_enter_blocking_section ();
+ CAMLreturnT (int, -1);
+ }
+
+ caml_enter_blocking_section ();
+ CAMLreturnT (int, Bool_val (rv));
+}
+
/*----------------------------------------------------------------------*/
/* set_* functions called from OCaml code at load time to initialize
* fields in the plugin struct.
@@ -792,6 +813,8 @@ SET(cache)
SET(thread_model)
+SET(can_fast_zero)
+
#undef SET
static void
@@ -836,6 +859,8 @@ remove_roots (void)
REMOVE (thread_model);
+ REMOVE (can_fast_zero);
+
#undef REMOVE
}
@@ -478,6 +478,9 @@ flags_string (uint32_t flags, char *buf, size_t len)
if (flags & NBDKIT_FLAG_REQ_ONE)
flag_append ("req_one", &comma, &buf, &len);
+
+ if (flags & NBDKIT_FLAG_FAST_ZERO)
+ flag_append("fast", &comma, &buf, &len);
}
static void
@@ -536,7 +539,7 @@ sh_pwrite (void *handle, const void *buf, uint32_t count, uint64_t offset,
/* Common code for handling all boolean methods like can_write etc. */
static int
-boolean_method (void *handle, const char *method_name)
+boolean_method (void *handle, const char *method_name, int def)
{
char *h = handle;
const char *args[] = { script, method_name, h, NULL };
@@ -546,8 +549,8 @@ boolean_method (void *handle, const char *method_name)
return 1;
case RET_FALSE: /* false */
return 0;
- case MISSING: /* missing => assume false */
- return 0;
+ case MISSING: /* missing => caller chooses default */
+ return def;
case ERROR: /* error cases */
return -1;
default: abort ();
@@ -557,37 +560,37 @@ boolean_method (void *handle, const char *method_name)
static int
sh_can_write (void *handle)
{
- return boolean_method (handle, "can_write");
+ return boolean_method (handle, "can_write", 0);
}
static int
sh_can_flush (void *handle)
{
- return boolean_method (handle, "can_flush");
+ return boolean_method (handle, "can_flush", 0);
}
static int
sh_is_rotational (void *handle)
{
- return boolean_method (handle, "is_rotational");
+ return boolean_method (handle, "is_rotational", 0);
}
static int
sh_can_trim (void *handle)
{
- return boolean_method (handle, "can_trim");
+ return boolean_method (handle, "can_trim", 0);
}
static int
sh_can_zero (void *handle)
{
- return boolean_method (handle, "can_zero");
+ return boolean_method (handle, "can_zero", 0);
}
static int
sh_can_extents (void *handle)
{
- return boolean_method (handle, "can_extents");
+ return boolean_method (handle, "can_extents", 0);
}
/* Not a boolean method, the method prints "none", "emulate" or "native". */
@@ -646,7 +649,7 @@ sh_can_fua (void *handle)
static int
sh_can_multi_conn (void *handle)
{
- return boolean_method (handle, "can_multi_conn");
+ return boolean_method (handle, "can_multi_conn", 0);
}
/* Not a boolean method, the method prints "none", "emulate" or "native". */
@@ -696,6 +699,21 @@ sh_can_cache (void *handle)
}
}
+static int
+sh_can_fast_zero (void *handle)
+{
+ int r = boolean_method (handle, "can_fast_zero", 2);
+ if (r < 2)
+ return r;
+ /* We need to duplicate the logic of plugins.c: if can_fast_zero is
+ * missing, we advertise fast fail support when can_zero is false.
+ */
+ r = sh_can_zero (handle);
+ if (r == -1)
+ return -1;
+ return !r;
+}
+
static int
sh_flush (void *handle, uint32_t flags)
{
@@ -962,6 +980,7 @@ static struct nbdkit_plugin plugin = {
.can_fua = sh_can_fua,
.can_multi_conn = sh_can_multi_conn,
.can_cache = sh_can_cache,
+ .can_fast_zero = sh_can_fast_zero,
.pread = sh_pread,
.pwrite = sh_pwrite,
@@ -96,6 +96,8 @@ type 'a plugin = {
cache : ('a -> int32 -> int64 -> flags -> unit) option;
thread_model : (unit -> thread_model) option;
+
+ can_fast_zero : ('a -> bool) option;
}
let default_callbacks = {
@@ -141,6 +143,8 @@ let default_callbacks = {
cache = None;
thread_model = None;
+
+ can_fast_zero = None;
}
external set_name : string -> unit = "ocaml_nbdkit_set_name" "noalloc"
@@ -186,6 +190,8 @@ external set_cache : ('a -> int32 -> int64 -> flags -> unit) -> unit = "ocaml_nb
external set_thread_model : (unit -> thread_model) -> unit = "ocaml_nbdkit_set_thread_model"
+external set_can_fast_zero : ('a -> bool) -> unit = "ocaml_nbdkit_set_can_fast_zero"
+
let may f = function None -> () | Some a -> f a
let register_plugin plugin =
@@ -249,7 +255,9 @@ let register_plugin plugin =
may set_can_cache plugin.can_cache;
may set_cache plugin.cache;
- may set_thread_model plugin.thread_model
+ may set_thread_model plugin.thread_model;
+
+ may set_can_fast_zero plugin.can_fast_zero
external _set_error : int -> unit = "ocaml_nbdkit_set_error" "noalloc"
@@ -101,6 +101,8 @@ type 'a plugin = {
cache : ('a -> int32 -> int64 -> flags -> unit) option;
thread_model : (unit -> thread_model) option;
+
+ can_fast_zero : ('a -> bool) option;
}
(** The plugin fields and callbacks. ['a] is the handle type. *)
@@ -105,6 +105,8 @@ pub struct Plugin {
flags: u32) -> c_int>,
pub thread_model: Option<extern fn () -> ThreadModel>,
+
+ pub can_fast_zero: Option<extern fn (h: *mut c_void) -> c_int>,
}
#[repr(C)]
@@ -163,6 +165,7 @@ impl Plugin {
can_cache: None,
cache: None,
thread_model: None,
+ can_fast_zero: None,
}
}
}
@@ -68,6 +68,7 @@ SEND_DF=$(( 1 << 7 ))
CAN_MULTI_CONN=$(( 1 << 8 ))
SEND_RESIZE=$(( 1 << 9 ))
SEND_CACHE=$(( 1 << 10 ))
+SEND_FAST_ZERO=$(( 1 << 11 ))
do_nbdkit ()
{
@@ -133,8 +134,8 @@ EOF
#----------------------------------------------------------------------
# can_write=true
#
-# NBD_FLAG_SEND_WRITE_ZEROES is set on writable connections
-# even when can_zero returns false, because nbdkit reckons it
+# NBD_FLAG_SEND_WRITE_ZEROES and NBD_FLAG_SEND_FAST_ZERO are set on writable
+# connections even when can_zero returns false, because nbdkit reckons it
# can emulate zeroing using pwrite.
do_nbdkit <<'EOF'
@@ -145,8 +146,8 @@ case "$1" in
esac
EOF
-[ $eflags -eq $(( HAS_FLAGS|SEND_WRITE_ZEROES|SEND_DF )) ] ||
- fail "$LINENO: expected HAS_FLAGS|SEND_WRITE_ZEROES|SEND_DF"
+[ $eflags -eq $(( HAS_FLAGS|SEND_WRITE_ZEROES|SEND_DF|SEND_FAST_ZERO )) ] ||
+ fail "$LINENO: expected HAS_FLAGS|SEND_WRITE_ZEROES|SEND_DF|SEND_FAST_ZERO"
#----------------------------------------------------------------------
# --filter=nozero
@@ -255,8 +256,8 @@ case "$1" in
esac
EOF
-[ $eflags -eq $(( HAS_FLAGS|SEND_TRIM|SEND_WRITE_ZEROES|SEND_DF )) ] ||
- fail "$LINENO: expected HAS_FLAGS|SEND_TRIM|SEND_WRITE_ZEROES|SEND_DF"
+[ $eflags -eq $(( HAS_FLAGS|SEND_TRIM|SEND_WRITE_ZEROES|SEND_DF|SEND_FAST_ZERO )) ] ||
+ fail "$LINENO: expected HAS_FLAGS|SEND_TRIM|SEND_WRITE_ZEROES|SEND_DF|SEND_FAST_ZERO"
#----------------------------------------------------------------------
# can_write=true
@@ -271,8 +272,8 @@ case "$1" in
esac
EOF
-[ $eflags -eq $(( HAS_FLAGS|ROTATIONAL|SEND_WRITE_ZEROES|SEND_DF )) ] ||
- fail "$LINENO: expected HAS_FLAGS|ROTATIONAL|SEND_WRITE_ZEROES|SEND_DF"
+[ $eflags -eq $(( HAS_FLAGS|ROTATIONAL|SEND_WRITE_ZEROES|SEND_DF|SEND_FAST_ZERO )) ] ||
+ fail "$LINENO: expected HAS_FLAGS|ROTATIONAL|SEND_WRITE_ZEROES|SEND_DF|SEND_FAST_ZERO"
#----------------------------------------------------------------------
# -r
@@ -304,8 +305,8 @@ case "$1" in
esac
EOF
-[ $eflags -eq $(( HAS_FLAGS|SEND_FUA|SEND_WRITE_ZEROES|SEND_DF )) ] ||
- fail "$LINENO: expected HAS_FLAGS|SEND_FUA|SEND_WRITE_ZEROES|SEND_DF"
+[ $eflags -eq $(( HAS_FLAGS|SEND_FUA|SEND_WRITE_ZEROES|SEND_DF|SEND_FAST_ZERO )) ] ||
+ fail "$LINENO: expected HAS_FLAGS|SEND_FUA|SEND_WRITE_ZEROES|SEND_DF|SEND_FAST_ZERO"
#----------------------------------------------------------------------
# -r
@@ -341,8 +342,8 @@ case "$1" in
esac
EOF
-[ $eflags -eq $(( HAS_FLAGS|SEND_FLUSH|SEND_FUA|SEND_WRITE_ZEROES|SEND_DF )) ] ||
- fail "$LINENO: expected HAS_FLAGS|SEND_FLUSH|SEND_FUA|SEND_WRITE_ZEROES|SEND_DF"
+[ $eflags -eq $(( HAS_FLAGS|SEND_FLUSH|SEND_FUA|SEND_WRITE_ZEROES|SEND_DF|SEND_FAST_ZERO )) ] ||
+ fail "$LINENO: expected HAS_FLAGS|SEND_FLUSH|SEND_FUA|SEND_WRITE_ZEROES|SEND_DF|SEND_FAST_ZERO"
#----------------------------------------------------------------------
# can_write=true
@@ -361,8 +362,8 @@ case "$1" in
esac
EOF
-[ $eflags -eq $(( HAS_FLAGS|SEND_FLUSH|SEND_WRITE_ZEROES|SEND_DF )) ] ||
- fail "$LINENO: expected HAS_FLAGS|SEND_FLUSH|SEND_WRITE_ZEROES|SEND_DF"
+[ $eflags -eq $(( HAS_FLAGS|SEND_FLUSH|SEND_WRITE_ZEROES|SEND_DF|SEND_FAST_ZERO )) ] ||
+ fail "$LINENO: expected HAS_FLAGS|SEND_FLUSH|SEND_WRITE_ZEROES|SEND_DF|SEND_FAST_ZERO"
#----------------------------------------------------------------------
# -r
@@ -448,3 +449,96 @@ EOF
[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|SEND_DF )) ] ||
fail "$LINENO: expected HAS_FLAGS|READ_ONLY|SEND_DF"
+
+#----------------------------------------------------------------------
+# -r
+# can_fast_zero=true
+#
+# Fast zero support isn't advertised without regular zero support
+
+do_nbdkit -r <<'EOF'
+case "$1" in
+ get_size) echo 1M ;;
+ can_fast_zero) exit 0 ;;
+ *) exit 2 ;;
+esac
+EOF
+
+[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|SEND_DF )) ] ||
+ fail "$LINENO: expected HAS_FLAGS|READ_ONLY|SEND_DF"
+
+#----------------------------------------------------------------------
+# --filter=nozero
+# can_write=true
+# can_fast_zero=true
+#
+# Fast zero support isn't advertised without regular zero support
+
+do_nbdkit --filter=nozero <<'EOF'
+case "$1" in
+ get_size) echo 1M ;;
+ can_write) exit 0 ;;
+ can_fast_zero) exit 0 ;;
+ *) exit 2 ;;
+esac
+EOF
+
+[ $eflags -eq $(( HAS_FLAGS|SEND_DF )) ] ||
+ fail "$LINENO: expected HAS_FLAGS|SEND_DF"
+
+#----------------------------------------------------------------------
+# can_write=true
+# can_zero=true
+#
+# Fast zero support is omitted for a plugin that has .zero but did not opt in
+
+do_nbdkit -r <<'EOF'
+case "$1" in
+ get_size) echo 1M ;;
+ can_write) exit 0 ;;
+ can_zero) exit 0 ;;
+ *) exit 2 ;;
+esac
+EOF
+
+[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|SEND_DF )) ] ||
+ fail "$LINENO: expected HAS_FLAGS|READ_ONLY|SEND_DF"
+
+#----------------------------------------------------------------------
+# can_write=true
+# can_zero=true
+# can_fast_zero=false
+#
+# Fast zero support is omitted if the plugin says so
+
+do_nbdkit -r <<'EOF'
+case "$1" in
+ get_size) echo 1M ;;
+ can_write) exit 0 ;;
+ can_zero) exit 0 ;;
+ can_fast_zero) exit 3 ;;
+ *) exit 2 ;;
+esac
+EOF
+
+[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|SEND_DF )) ] ||
+ fail "$LINENO: expected HAS_FLAGS|READ_ONLY|SEND_DF"
+
+#----------------------------------------------------------------------
+# can_write=true
+# can_zero=false
+# can_fast_zero=false
+#
+# Fast zero support is omitted if the plugin says so
+
+do_nbdkit -r <<'EOF'
+case "$1" in
+ get_size) echo 1M ;;
+ can_write) exit 0 ;;
+ can_fast_zero) exit 3 ;;
+ *) exit 2 ;;
+esac
+EOF
+
+[ $eflags -eq $(( HAS_FLAGS|READ_ONLY|SEND_DF )) ] ||
+ fail "$LINENO: expected HAS_FLAGS|READ_ONLY|SEND_DF"
Allow plugins to affect the handling of the new NBD_CMD_FLAG_FAST_ZERO flag, then update affected plugins. In particular, in-memory plugins are always fast; the full plugin is better served by omitting .zero and relying on .pwrite fallback; nbd takes advantage of libnbd extensions proposed in parallel to pass through support; and v2 language bindings expose the choice to their scripts. The testsuite is updated thanks to the sh plugin to cover this. In turn, the sh plugin has to be a bit smarter about handling missing can_fast_zero to get decent fallback support from nbdkit. Plugins untouched by this patch either do not support .zero with flags (including v1 plugins; these are all okay with the default behavior of advertising but always failing fast zeroes), or are too difficult to analyze in this patch (so not advertising is easier than having to decide - in particular, the file plugin is tricky, since BLKZEROOUT is not reliably fast). The nozero filter can be used to adjust fast zero settings for a plugin that has not yet updated. Signed-off-by: Eric Blake <eblake@redhat.com> --- docs/nbdkit-plugin.pod | 74 +++++++++++++++---- plugins/sh/nbdkit-sh-plugin.pod | 13 +++- server/plugins.c | 25 +++++-- include/nbdkit-plugin.h | 2 + plugins/data/data.c | 14 +++- plugins/full/full.c | 12 ++-- plugins/memory/memory.c | 14 +++- plugins/nbd/nbd.c | 28 +++++++- plugins/null/null.c | 8 +++ plugins/ocaml/ocaml.c | 25 +++++++ plugins/sh/sh.c | 39 +++++++--- plugins/ocaml/NBDKit.ml | 10 ++- plugins/ocaml/NBDKit.mli | 2 + plugins/rust/src/lib.rs | 3 + tests/test-eflags.sh | 122 ++++++++++++++++++++++++++++---- 15 files changed, 332 insertions(+), 59 deletions(-)